An electrolyte is known in the art for gold-plating which has the following composition, g/l:
______________________________________ hexapotassium-m-ethylenediaminetetraacetato- 10.5-123 bis-(aurous sulphite) K.sub.6 [Au.sub.2 (SO.sub.2).sub.2 Edta] alkali metal salts of ethylenediamine- 17.8-140 tetraacetic acid Me.sub.4 Edta potassium sulphate K.sub.2 SO.sub.4 12.6-110 bisubstituted potassium phosphate K.sub.2 HPO.sub.4 4.7-40 distilled water the balance. ______________________________________
(Cf. USSR Inventor's Certificate No. 666920, Cl. C 25 D 3/48, 1976; U.S. Pat. No. 4,212,708; Cl. 204-43G).
Also known is a process for the preparation of the above specified electrolyte comprising precipitation, from an aqueous solution of chloroauric acid by means of disubstituted ammonium phosphate, of a sparingly soluble gold compound--bis-(dihydrophosphatomonohydrophosphato)-aurate of ammonium; the residue is washed to remove chloride ions and then dissolved by addition to an aqueous solution of disodium salt of ethylenediaminetetraacetic acid, caustic potash and potassium sulphite (see the opt.cit. reference).
This process is a multi-staged one which results in irrevocable mechanical loss of gold. Furthermore this process gives an electrolyte containing bisubstituted potassium phosphate and potassium sulphate. Upon correction of the electrolyte bath by the electrolyte of the above-specified composition, these substances are accumulated in the bath, thus affecting the course of the gold-plating process.
This process does enable the production of an electrolyte with a content of hexapotassium-m-ethylenediaminetetraacetatobis-(aurous sulphite /I/) above 123 g/l. The impossibility of increasing, in the electrolyte, the content of hexapotassium-m-ethylenediaminetetraacetatobis-(aurous sulphite), as well as the presence of contaminants of bisubstituted potassium phosphate and potassium sulphate limits the scope of application of the above-mentioned electrolyte.